1. Field of the Invention
The invention relates to a storage device for a liquid medium that is received in a receiving chamber of a housing and separated by at least one partitioning element from a chamber filled at least partially with a gas that is under pressure and keeps the liquid medium in the receiving chamber under pressure.
2. Description of the Related Art
In the automotive field, piston and membrane storage devices are used which have two separate variable volume chambers separated from one another by a piston or a membrane or diaphragm. The storage device serves as a reservoir for a liquid medium, usually oil, contained in a first one of the chambers and maintained under pressure by a gas located in the second chamber. The storage devices can be adapted by variation of their size and the preload pressure of the gas to different requirements and conditions of use. Depending on the temperature and the pressure range, the piston as well as the membrane are prone to leak, i.e., the gas escapes from the gas chamber via the piston seal or by diffusion via the membrane. Particularly membrane storage devices are very susceptible to diffusion. By providing multi-layer membranes, diffusion can be reduced; however, it cannot be completely prevented. Accordingly, over the service life of the storage device the gas pressure in both systems will decrease gradually; this leads to a limitation of the usable pressure range and a reduction of the available storage volume. Large temperature differences in operation, combined with large piston or membrane movements, increase gas loss. In addition, the membrane is susceptible to tearing in the case of large deformations at low temperatures. Conventional gases are, for example, nitrogen (N2) or carbon tetrafluoride (CF4) as well as a mixture of these gases. The gas to be used is selected depending on the range of temperature of the respective application as well as the permissible diffusion, i.e., the permissible gas loss over the service life of the device. The materials of the piston seal and of the membrane must be matched to the media employed in the device. Otherwise, depending on the medium, swelling of the seal or gasket or failure of the membrane can be the result.